96% of the 541000 coffee growing families rely on sun/solar drying to process the coffee. Nevertheless, in Colombia, the harvest seasons are coincident with the rainy seasons, not the most suitable condition to dry coffee using sun energy and natural convection.
Small mechanical coffee dryers emerged as a solution for these issues, however, these units are usually expensive and require grid connection to run the fan and LPG to heat the drying air. Therefore, their running costs and working principles could be difficult to achieve due to the isolated nature of some farms.
Due to these reasons, the wet commercialization of coffee has been growing rapidly in the country, yet, the farmers are still in disadvantage since the buying prices are lower. Hence, the idea of providing a sustainable solution through a hybrid solar dryer, that integrates mechanical drying powered by photovoltaic panels and uses residual biomass from the coffee processing as biofuel came as a solution to the problem.
The unit allows to work 24/7 mixing mechanical and solar drying, solar during the day and mechanical during the night and fully solar, reducing the drying times significantly while preserving the product's quality.
The dryer uses coffee trunks and other residual biomass as fuel. With an integrated heat exchanger, the unit uses the thermal energy from the combustion of biomass to heat the drying air.
The electricity demand from the fan is achieved by a PV system featuring 2 panels, one charge controller, inverter and a battery to store energy and provide supply during the nighttime.